The present invention relates to the printing of webs, particularly but not exclusively of textile webs. More particularly, the invention relates to an apparatus for printing such webs.
The printing of webs is well known in the prior art and can be carried out in a variety of ways, for example by offset printing, by screen printing, by rotary printing or the like. In all of the prior-art proposals, however, the pattern to be printed onto the web is formed in toto on a printing element, for example in form of a plurality of perforations in a printing screen of a screen printing machine. Once the pattern is first applied, for example once the perforations are formed in the screen during manufacture of the screen, it is to all intents and purposes unchangeable and if a different pattern is to be printed, a new printing element, e.g. a new printing screen, must be installed in the mahcine.
This has very evident disadvantages, particularly in modern times in which a large and rapid change in the types of patterns is desired, and is often dictated by rapid changes in fashion. Under these circumstances, the necessary change of the printing element for each change of the pattern to be printed, results in an enormous increase in operating costs. Moreover, in view of the fact that a complete change-over of the printing element is so expensive, e.g. a printing screen with a new pattern costs approximately $25,000.00 or more, an economically viable manufacturing operation is possible only if large or very large quantities of webs are to be printed with one and the same pattern. In operations in which relatively small quantities of webs are to be printed, which occurs often in the present-day fashion climate, the purchase costs of obtaining a different printing element for each different pattern to be printed, are often completely prohibitive.
All prior-art printing methods can basically be subdivided into two categories, namely rotary printing and flat printing. In all of these applications the disadvantages outlined above obtain fully and without reservation. If the pattern is to be changed, then the printing element must be replaced with a different one. If some correction in the pattern is to be carried out, which occurs relatively frequently, but is not of such magnitude that the whole printing element must be replaced, then extremely complicated manual labor must be performed to carry out the correction, which is again highly labor- and cost-intensive and severely depresses the economic feasibility of the operation.
It has been proposed in the prior art to spray printing medium onto the workpiece web from nozzles. However, according to this proposal the printing medium must be atomized and once it leaves the nozzles is completely uncontrolled. This means that the printing medium impinging the workpiece web can at best produce a very rough pattern but will not, however, be able to produce an exact pattern or contour. The material produced in this way is of very inferior quality and is not acceptable to quality-oriented consumers.